ADDRESS. xxi 
basis: and the degree of progress at which ‘animality’ can be predicated, 
is ‘on a par’ with that at which ‘ vegetality’ can be predicated. Then follow 
other steps of complexity, by which plants and animals diverge from each 
other as they rise in the scale of perfection. 
The experiments of Trembley on the freshwater polype, those of Spal- 
lanzani on the Naiads, and those of Bonnet on the Aphides, had brought to 
light the phenomena of propagation by fission, and by gemmation or buds, 
external and internal, in animals, to which Hunter refers. Subsequent research 
has shown the unexpected extent to which Hunter's first principle of pro- 
pagation in organic beings prevails in the animal division. But the earliest 
formal supersession of Harvey’s axiom, ‘omne vivum ab ovo, appears to be 
Hunter's proposition of the dual principle above quoted. Bacon readily 
accepted, as, indeed, it was congenial with his physiological philosophy, the 
doctrine current in his day of the spontaneous origin of worms, insects, eels, 
and other ‘creeping things.’ But this doctrine receives no countenance from 
the modification of the Harveian dictum introduced by the great English 
physiologist of the last century. 
The experiments of Redi, Malpighi, and others, had progressively con- 
tracted the field to which the ‘ generatio eequivoca’ could with any plausibility 
be applied. The stronghold of the remaining advocates of that old Egyptian 
doctrine was the fact of the development of parasitic animals in the flesh, 
brain and glands of higher animals. But the hypothesis never obtained 
currency in this country ; it was publicly opposed in my ‘Hunterian Lec- 
tures,’ by the fact of the prodigious preparation of fertile eggs in many of 
the supposed spontaneously developed species; and in then suggesting that 
the ‘ Trichina spiralis’ of the human muscular tissue might be the embryo 
of a larger worm in course of migration, I urged that a particular investiga- 
tion was needed for each particular species*. Among the most brilliant of 
recent acquisitions to this part of physiology have been the discoveries which 
have resulted from such special investigations. Kuchenmeister and Von . 
Siebold have been the chief labourers in this field. I may instance a few 
of their results. 
The ‘thread-worms’ (Filarie) of certain insects, which present no trace 
of sexual organs, were supposed to be spontaneously developed in those in- 
sects. The little worms were, however, by special and due research, seen to 
wind their way out of the caterpillars they infested. Von Siebold placed 
these free Filarie in damp earth, into which they soon bored: in a few 
weeks he found that the sexual organs were developed in them, and that 
they laid hundreds of eggs. Early in spring the young worms were hatched 
and began to creep about. Von Siebold took some young caterpillars of 
the moth ( Yponomeuta euonymella), in which were no parasites: he placed 
them in the soft earth in which the young Filarie had been hatched; and 
in twenty-four hours most of the caterpillars were infested by the young 
~ * Hunterian Lectures, reported in ‘ Medical Times.’ 
